1. Field of the Invention
The present invention relates to an illumination device used in a keyboard, etc., which is an input section of a computer, and an illuminated input device such as a keyboard in which the illumination device is installed.
2. Description of the Background Art
There exist various types of illuminated input devices (e.g., a keyboard in which an illumination device is installed) for allowing a user to use a computer, or the like, in poorly lit places or at night. For example, in an illuminated input device disclosed in U.S. Pat. No. 6,284,988 and Japanese Patent Laid-Open Publication No. 2002-251937, an electroluminescence (EL) sheet is used in the keyboard; light emitted therefrom passes through translucent key tops and illuminates all input keys.
Also, in an illuminated input device disclosed in Japanese Patent Laid-Open Publication No. H7-73777, each input key of the keyboard is provided with a light emitting member. Specifically, light from the light emitting member such as a light emitting diode (LED), which is placed just under each translucent key top, passes through the key top, and emphasizes characters and numbers on the key tops, thereby increasing visibility in low light conditions.
Also, Japanese Patent Laid-Open Publication No. H9-319481 discloses an illuminated input device provided with a light source, which is placed in a position away from the input keys, and a light guiding path to each input key. In this illuminated input device, a light source such as a light emitting diode is placed in a space between the key tops, and a light guiding path is formed therefrom to four surrounding key tops. Light is guided to each key top from the four light guiding paths surrounding the key top. A translucent resin capable of diffusing light is used as a material for the key top. Thus, the key tops are illuminated evenly. In this case, the number of necessary light sources is nearly equal to the number of key tops.
Furthermore, Japanese Patent Laid-Open Publication No. 2002-251937 discloses an illuminated input device illuminating the entire keyboard. This illuminated input device uses an EL sheet as a light emitter, thereby illuminating the entire keyboard with a single light source.
The EL sheet adopted in the illuminated input device disclosed in U.S. Pat. No. 6,284,988 and Japanese Patent Laid-Open Publication No. 2002-251937 has the following disadvantages as compared to other light sources: the EL sheet is expensive and requires increased production cost due to the need of an inverter circuit as a driving unit, requires a measurable amount of power, and high running costs due to its short life span, produces an uncomfortable vibration noise while the light is on, and poorly illuminates the keyboard due to its low illuminance, which is about one tenth of the illuminance of the LED.
On the other hand, the illuminated input device disclosed in Japanese Patent Laid-Open Publication No. H7-73777 and Japanese Patent Laid-Open Publication No. H9-319481 requires an amount of light sources equal to almost as many as the number of key tops of the input keys. Specifically, even if the LED adopted in the above illuminated input device is an inexpensive light source compared to the EL sheet, there is the need to use as many LEDs as key tops (whose number is about 80 to 90). Thus, the production cost of the keyboard is increased due to an increased cost of the light source and an increased number of stages in the assembly process of the keyboard.